Depletion type floating gate p-channel MOS transistor for recording action potentials generated by cultured neurons

We report the realization of electrical coupling between neurons and depletion type floating gate (FG) p-channel MOS transistors. The devices were realized in a shortened 0.5 μm CMOS technology. Increased boron implant dose was used to form the depletion type devices. Post-CMOS processing steps were added to expose the devices sensing area. The neurons are coupled to the polycrystalline silicon (PS) FG through 420 Å thermal oxide in an area which is located over the thick field oxide away from the transistor. The combination of coupling area pad having a diameter of 10 or 15 μm and sensing transistor with W/L of 50/0.5 μm results in capacitive coupling ratio of the neuron signal of about 0.5 together with relatively large transistor transconductance. The combination of the FG structure with a depletion type device, leads to the following advantages. (a) No need for dc bias between the solution in which the neurons are cultured and the transistor with expected consequences to the neuron as well as the silicon die durability. (b) The sensing area of the neuron activity is separated from the active area of the transistor. Thus, it is possible to design the sensing area and the channel area separately. (c) The channel area, which is the most sensitive part of the transistor, can be insulated and shielded from the ionic solution in which the neurons are cultured. (d) There is an option to add a switching transistor to the FG and use the FG also for the neuron stimulation.     

The Yck2 yeast casein kinase 1 isoform shows cell cycle-specific localization to sites of polarized growth and is required for proper septin organization

Casein kinase 1 protein kinases are ubiquitous and abundant Ser/Thr-specific protein kinases with activity on acidic substrates. In yeast, the products of the redundant YCK1 and YCK2 genes are together essential for cell viability. Mutants deficient for these proteins display defects in cellular morphogenesis, cytokinesis, and endocytosis. Yck1p and Yck2p are peripheral plasma membrane proteins, and we report here that the localization of Yck2p within the membrane is dynamic through the cell cycle. Using a functional green fluorescent protein (GFP) fusion, we have observed that Yck2p is concentrated at sites of polarized growth during bud morphogenesis. At cytokinesis, GFP-Yck2p becomes associated with a ring at the bud neck and then appears as a patch of fluorescence, apparently coincident with the dividing membranes. The bud neck association of Yck2p at cytokinesis does not require an intact septin ring, and septin assembly is altered in a Yck-deficient mutant. The sites of GFP-Yck2p concentration and the defects observed for Yck-deficient cells together suggest that Yck plays distinct roles in morphogenesis and cytokinesis that are effected by differential localization.     

Specific induction and carbon/nitrogen repression of arginine catabolism gene of Aspergillus nidulans--functional in vivo analysis of the otaA promoter

The arginine catabolism gene otaA encoding ornithine transaminase (OTAse) is specifically induced by arginine and is under the control of the broad-domain carbon and nitrogen repression systems. Arginine induction is mediated by a product of arcA gene coding for Zn(2)C(6) activator. We have identified a region responsible for arginine induction in the otaA promoter (AnUAS(arg)). Deletions within this region result in non-inducibility of OTAse by arginine, whether in an arcA(+) strain or in the presence of the arcA(d)47 gain of function allele. AnUAS(arg) is very similar to the Saccharomyces cerevisiae UAS(arg), a sequence bound by the Zn(2)C(6) activator (ArgRIIp), acting in a complex with two MADS-box proteins (McmIp and ArgRIp).We demonstrate here that two CREA in vitro binding sites in the otaA promoter are functional in vivo. CREA is directly involved in carbon repression of the otaA gene and it also reduces its basal level of expression. Although AREA binds to the otaA promoter in vitro, it probably does not participate in nitrogen metabolite repression of the gene in vivo. We show here that another putative negatively acting GATA factor AREB participates directly or indirectly in otaA nitrogen repression. We also demonstrate that the high levels of OTAse activity are an important factor in the suppression of proline auxotrophic mutations. This suppression can be achieved neither by growing of the proline auxotroph under carbon/nitrogen derepressing conditions nor by introducing of a creA(d) mutation.     

Daily variations in the influence of noradrenaline on preferred ambient temperature of the Siberian hamster

Daily variations in sensitivity to noradrenaline (NA) and the activation of nonshivering thermogenesis (NST) are important for survival under a potentially wide range of environmental conditions. However, little is known regarding the ability of the Siberian hamster and other species to activate NST in the day and night when they may be subjected to marked variations in environmental temperature. In this study, the effects of acclimation temperature and time of day on the behavioral thermoregulatory response to NA injections in Siberian hamsters (Phodopus sungorus) was investigated. Hamsters were acclimated for 4 weeks to 23 degrees C and a L:D 12:12 h photoperiod. After acclimation, preferred ambient temperatures (PT(a)) in saline- and NA-injected animals were measured continuously in the temperature gradient system. NA (0.6 mg/kg; s.c.) was given every 4 h while PT(a) was monitored. After NA injections there was a rapid drop in PT(a), decreasing to approximately 15 degrees C within 10-20 min after each NA injection. Following 4 weeks of acclimation to 10 degrees C and a L:D 8:16 h photoperiod, the same hamsters were re-tested in the temperature gradient system. Cold acclimation led to an accentuation in the behavioral response with a decrease in PT(a) of approximately 10 degrees C. The maximal decrease in preferred ambient temperatures was recorded during the light phase of the day and during the second part of the night. Lowering of PT(a) after NA allows for rapid dissipation of the heat from NST. Overall, the behavioral response reflects the daily changes in brown adipose tissue sensitivity to NA and thus capacity for NST.     

The role of glutathione in yeast dehydration tolerance

Among the factors that affect cell resistance against dehydration, oxidation is considered to be of great importance. In this work, we verified that both control and glutathione deficient mutant strains were much more oxidized after dehydration. Moreover, cells lacking glutathione showed a twofold higher increase in oxidation and lipid peroxidation than the control strain. While glucose 6-phosphate dehydrogenase and glutathione reductase activities did not change in response to dehydration in the control strain, the mutant strain gsh1 (glutathione deficient) showed a reduction of 50% in both activities, which could explain the high levels of oxidation shown by gsh1 cells. In conformity with these results, the mutant lacking GSH1 showed a high sensitivity to dehydration. Furthermore, the addition of glutathione to gsh1 cells restored survival rates to the levels of the control strain. We conclude that glutathione plays a significant role in the maintenance of intracellular redox balance during dehydration.     

Cross-resistance to five glucocorticoids in childhood acute lymphoblastic and non-lymphoblastic leukemia samples tested by the MTT assay: preliminary report

In vitro antileukemic activity of five glucocorticoids and their cross-resistance pattern in childhood acute lymphoblastic and non-lymphoblastic leukemia were determined by means of the MTT assay in 25 leukemia cell samples of childhood acute leukemias. The equivalent antileukemic concentrations of the drugs tested were: 34 microM hydrocortisone (HC), 8 microM prednisolone (PRE), 1.5 microM methylprednisolone (MPR), 0.44 microM dexamethasone (DX) and 0.22 microM betamethasone (BET). In comparison with initial ALL cell samples, the relapsed ALL group was more resistant to PRE (38-fold, p = 0.044), DX (> 34-fold, p = 0.04), MPR (38-fold), BET (45-fold) and HC (33-fold). The AML cell samples were even more resistant to: PRE (> 85-fold, p = 0.001), DX (> 34-fold, p = 0.004), MPR (> 69-fold, p = 0.036), BET (> 69-fold, p = 0.038) and HC (54-fold, p = 0.059) when compared with ALL on initial diagnosis. A significant cross-resistance among all the glucocorticoids used was found. Only in some individual cases the cross-resistance was less pronounced.